【摘要】 对纳米晶钆(Gd)和镝(Dy)块体材料的磁性进行了研究。与多晶比较,通常纳米晶的磁化强度减小,居里温度TC降低,但平均粒径为10 nm的纳米晶Dy的居里温度TC反而升高到100 K,平均粒径为10 nm的纳米晶Gd中还存在明显的反铁磁相。通过RKKY交换作用的计算知道,晶面晶界处原子的交换积分会发生正负号的变化,能量最低的稳定状态对应三种有序相:铁磁相、反铁磁相和扇相,晶粒中在一定条件下出现三相共存。对于平均粒径为10 nm的纳米晶,晶面晶界处原子所占比例很大,三相叠加的结果,对于Gd,即是在相变点附近出现磁化强度尖峰;对于Dy,则是磁化强度随温度升高下降缓慢,表现为居里温度TC比多晶升高。更多还原

【Abstract】 The magnetic properties of bulk nanocrystalline metal gadolinium(Gd) and dysprosium(Dy) samples were studied.The magnetization and Curie temperature TC of nanocrystalline Gd and Dy decreased usually as compared with the polycrystal.However,when the mean grain size was 10 nm,the Curie temperature TC of nanocrystalline Dy increased to 100 K instead and there was an antiferromagnetic phase in nanocrystalline Gd.According to the calculation based on Ruderman-Kittel-Kasuya-Yosida exchange interaction,the exchange integral of the grain boundary atoms and crystalline surface atoms had its sign changed from plus to minus or vice versa,and there were three orderly phases in the steady state with the lowest energy,ferromagnetic phase,antiferromagnetic phase and fan phase.For the nanocrystals with mean grain size of 10 nm,the proportion of grain boundary to crystalline surface atoms was high,and as the result of superposition of the three phases,and there appeared a peak near the phase transition temperature for the nanocrystalline Gd.While for the Dy,the magnetization decreased gently with temperature,and showing a higher Curie temperature than in the case of the polycrystal.更多还原